Approximately 1 in 3 Americans will eventually develop cancer, and as of January 1990 approximately 122,000 cases of AIDS had been reported to the CDC. The traumatic changes that occur in the lives of persons diagnosed with either of these illnesses call for coping strategies beyond those used in everyday life, and they have important implications for the mental health of both the patient and family members. Therefore, these individuals are at high risk for the development of psychosocial problems secondary to the illness. The purpose of the proposed longitudinal, prospective study is to test a model of adaptation to life-threatening illness that provides a framework for understanding adaptation as a process from perception of the stressor to social and behavioral outcomes. Two comparison groups will be used that, include 120 persons with cancer and 120 persons with AIDS at T1. The three data points will be 1 month, 6 months, and 12 months following a: diagnosis of cancer or the onset of CDC AIDS. Both the quantitative and qualitative data will be obtained to examine relationships among the variables included in the model. Regression will be the primary statistical approach used to evaluate relationships at each data point, as well as across time. A primary purpose of the analysis will be to identify those variables associated with positive social and behavioral adaptation.